LADY GAGA APOLOGIZES FOR COLLAB W/ R. KELLY Pulling Song From iTunes

Lady Gaga's sorry she ever worked with R. Kelly, saying she's going to pull their 2013 track from iTunes and other streaming services as an act of solidarity with the women he allegedly abused.

Gaga spoke out against Kelly early Thursday morn, saying the claims against him are "absolutely horrifying and indefensible" ... and she stands behind the women 1000%.

She says her single with Kelly, called "Do What U Want (With My Body)," came at a dark time in her life -- when her thinking was "explicitly twisted" because she was dealing with the trauma of being a sexual assault survivor herself.

Lady Gaga says she's grown and gotten help since then, and vows going forward to "continue to support women, men and people of all sexual identities, and of all races, who are victims of sexual assault."

She plans to remove the 2013 collab with Kelly online and adds ... "I'm sorry, both for my poor judgment when I was young, and for not speaking out sooner." Interestingly, since posting her plan to pull the track, it's been purchased and streamed way more. Seems like people are getting their last licks.

As you know ... Gaga's statement comes on the heels of major controversy involving Lifetime's docuseries, "Surviving R. Kelly," in which he's accused of sexual abuse, pedophilia and predatory behavior.

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She'd been mum on the subject until now and taken some heat for it ... especially since she's very much in the public eye right now with all the awards season buzz for "A Star is Born."

In fact, Gaga won Best Actress at the National Board of Review Awards Wednesday night in NYC ... and spoke out against Kelly hours later.